To stimulate subterranean formations to enhance oil and gas production, fluid is pumped from the surface into an oil or gas bearing sub-surface at a rate and pressure sufficient, e.g. about 34 MPa-48.2 MPa, to cause a fracture of the subterranean formations. This process is commonly referred to as hydraulic fracturing. In a hydraulic fracturing process, proppant particulates (usually sand) are blended into the fluid and injected into the formation to fill and prop open the underground fracture to maintain the fracture in an open condition. The proppants create a permeable pathway through which oil and gas can flow into the oil bore. However, if the proppant particles pulverize in the fracture, then the resulting fines will reduce the flow of oil and gas flowing into the oil bore. And, if the proppant particles break free and flow with the oil and gas into the oil bore, then the hydraulically formed fractures can close and reduce the productivity of the well.
To prepare proppant particulates for hydraulic fracturing process, epoxy resin coatings have been used to coat proppant particulates. There are a number of patents teaching the use of epoxy coatings for proppants. Some of the patents describing the epoxy coatings are U.S. Pat. No. 3,854,533; U.S. Pat. No. 3,867,986; U.S. Pat. No. 4,829,100; U.S. Pat. No. 4,869,960; and U.S. Pat. No. 5,422,183.
A number of approaches have been used to minimize coating proppant fracture, disintegration, and the resulting fines. U.S. Patent Publication No. 2006/0035790 and U.S. Pat. No. 5,697,440 discuss the use of elastomeric coatings. U.S. Pat. No. 6,172,011 discusses incorporating fibrous materials on the proppant particulates. U.S. Pat. No. 5,604,184 discloses a method for opening a subsurface fracture using chemically inert resin coated proppant particulates. U.S. Pat. Nos. 5,871,049 and 6,209,643 describe the use of a tackifying compound with the proppant particulates. U.S. Patent Publication No. 2005/0194141 discloses the use of soluble fibers in the resin coating of the proppant particulates. U.S. Pat. No. 5,837,656 and U.S. Patent Publication No 2003/0224165 disclose the use of multilayer coatings on the proppant particulates. All of these teachings disclose the use of an additional raw material or an additional step in the process to minimize the generation of fines due to pulverization and brittle failure of the proppant particulates under pressure.
Proppant particles are epoxy coated by the process of blending proppant particles with a liquid mixture comprising an epoxy resin and an epoxy hardening agent at an elevated temperature until a free flowing coated proppant is produced. Despite the significant benefits provided by epoxy coated proppants, the process used to make epoxy coated proppants is complicated by the required liquid/solid processing.